The retroviral enzyme, integrase (IN) catalyzes the insertion of newly synthesized viral DNA into the host cell chromatin. As DNA integration is required for efficient viral replication, IN is an attractive target for rational drug design. Such efforts are currently limited by an incomplete knowledge of IN structure and the manner in which IN interacts with DNA substrates. Thus, one major goal of the research described is to obtain a more detailed understanding of the molecular structure of IN and its interaction with DNA. Aim 1 will use X-ray crystallography to analyze HIV IN bound to DNA substrates designed to stabilize the complexes. The contribution of the C-terminal domain to DNA binding will be investigated by NMR spectroscopy and biochemical methods. A second goal is to exploit inhibitory HIV IN antibodies, developed and characterized in the P.l.'s laboratory, to investigate protein conformation and function. Aim 2 will optimize conditions for crystallization of a complex that includes full-length IN and a C-terminal-directed monoclonal Fab; its analysis will provide further details of IN structure and the mechanism of inhibition by this antibody. In addition, amino acid substitutions will be introduced into HIV-1 IN to test specific structure-based hypotheses concerning inhibition by the C-terminal- as well as an N-terminal-directed antibody, based on molecular models of IN-Fab complexes. The Specific Aims of this proposal build upon the extensive experience and technical expertise of the P.I. and collaborators, and the discoveries made in the P.l.'s laboratory during the last funding period. The knowledge gained will increase understanding of the structure and function of IN, and suggest new strategies to inhibit this essential viral enzyme.